JP2000153288A - Rotating disk type sewage treating device and rotating disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotating disk type sewage treating device and a rotating disk excellent in sewage treating performance and capable of reducing the cost. SOLUTION: In the rotating disk type sewage treating device in which plural sheets of the rotating disks 1 and 1 are attached to a rotary shaft 3 with a an interval and each of rotating disks 1 and 1 is provided so as to partially immersed and rotate in the sewage in a treating tank and the sewage is brought into contact with the aerobic bacteria stuck to the rotating disk 1 and treated, the net part 19a and 19b formed by arranging side by side many small piece members 191 different in direction are provided at each rotating disk 1, and a projection 192 is provided projectingly at the crossing part of the small piece member 191 with each other and the projection 192 provided projectingly at one side rotating disk 1 of two sheets of adjacent rotating disk is turned to the space between the small piece member 191 of the net part of the other side rotating disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotating disk type sewage treatment apparatus and a rotating disk.

[0002]

2. Description of the Related Art Conventionally, as described in, for example, JP-A-6-98184, a plurality of rotating disks are mounted on a rotating shaft at intervals, and each rotating disk is disposed in a processing tank. 2. Description of the Related Art There is known a rotating disk type sewage treatment apparatus which is provided so as to be partially immersed in sewage and rotates, and in which sewage comes into contact with aerobic bacteria attached to a rotating disk to treat sewage.

Conventionally, a sewage treatment apparatus has been required to be able to treat sewage efficiently, to have a low initial investment, to have a low operation and maintenance cost, and to have easy operation management. In principle, the required conditions of the sewage treatment apparatus are satisfied.

[0004]

However, in the conventional rotary disk type sewage treatment apparatus, the degree of contact of the sewage in the sewage treatment tank with the aerobic bacteria adhering to the rotary disk is small, and in practice, the cost is high. In addition, the processing performance was not always satisfactory.

The present invention has been made in view of such problems in the conventional rotating disk type sewage treatment apparatus, and has an object to solve the problems in the conventional rotating disk type sewage processing apparatus. It is an object of the present invention to provide a rotating disk type sewage treatment apparatus and a rotating disk which can solve the above problems, have excellent sewage treatment performance, and can reduce the cost.

[0006]

In order to achieve the above-mentioned object, a rotating disk type sewage treatment apparatus according to the present invention according to claim 1, wherein a plurality of rotating disks are attached to a rotating shaft at intervals. A rotating disk type sewage is provided in which each rotating disk is partially immersed in the sewage in the treatment tank and rotates, and the sewage comes into contact with aerobic bacteria adhering to the rotating disk and the sewage is treated. In the processing apparatus, each rotating disk is provided with a mesh portion formed by juxtaposing a plurality of strip members having different directions, and a projection is protruded at an intersection of the strip members to be adjacent to each other. The protrusion protruding from one of the two rotating disks is directed toward the space between the strip members of the net portion of the other rotating disk.

The rotating disk according to the present invention described in claim 2 is:
A rotary disk used in the rotary disk type sewage treatment apparatus according to claim 1, wherein each rotary disk is provided with a net portion formed by juxtaposing a plurality of strip members having different directions. A projection is provided at an intersection of the one member.

The rotating disk according to the present invention described in claim 3 is
2. A rotary disk used in the sewage treatment apparatus according to claim 1, wherein each rotary disk is provided with a net portion formed by juxtaposing a plurality of strip members having different directions. At the intersection of the projections, a large number of strip members are arranged in a vertical and horizontal lattice substantially perpendicular to the radiation direction and the radiation direction, and a diagonal lattice mesh substantially perpendicular to the radiation direction and orthogonal to each other. Are provided.

In the present invention, the material of the rotating disk may be any of those conventionally used for the material of the rotating disk, and is not particularly limited.
Synthetic resins such as vinyl chloride resin, polyethylene, polypropylene, polycarbonate, and FRP, and metals such as stainless steel and aluminum can be used.

In the rotary disk type sewage treatment apparatus according to the present invention, each rotary disk is provided with a net portion formed by juxtaposing a plurality of strip members having different directions. A projection is provided at the intersection of the strip members, and the projection provided on one of the two rotating disks is formed between the strip members of the mesh of the other rotating disk. Since it is directed in the direction of space, it has the following effect. That is, the efficiency of sewage treatment is high for the following reasons. The surface area per unit volume of the rotating disk is large. Since the water flow in the axial direction is not hindered, the number of treatment stages is substantially large. A large amount of oxygen is supplied to the wastewater due to the aeration effect of the protrusions on the disk. Abundant biofilms with macro transport phenomena. In addition, the stability of sewage treatment is high for the following reasons. There is no deterioration of treated water due to simultaneous detachment of biofilm from the disk surface. The gaps between the biofilms are formed uniformly, and there is no clogging due to excessive adhesion of the biofilm.

Further, in the rotating disk according to the present invention, each rotating disk is provided with a mesh portion formed by arranging a number of strip members having different directions in parallel. Since the projection is provided at the intersection of, there is the following operation in use. That is, the efficiency of sewage treatment is high for the following reasons. The surface area per unit volume of the rotating disk is large. Since the water flow in the axial direction is not hindered, the number of treatment stages is substantially large. A large amount of oxygen is supplied to the wastewater due to the aeration effect of the protrusions on the disk. Abundant biofilms with macro transport phenomena. In addition, the stability of sewage treatment is high for the following reasons. There is no deterioration of treated water due to simultaneous detachment of biofilm from the disk surface. The gaps between the biofilms are formed uniformly, and there is no clogging due to excessive adhesion of the biofilm. In addition, the same kind of rotating disk is used, and the processing device according to claim 1 can be obtained by appropriately arranging the projections of the adjacent ones, so that it can be formed by a single type of mold.

Further, in the rotating disk according to the present invention, each rotating disk is provided with a mesh portion formed by juxtaposing a plurality of strip members having different directions. Projections are projected at the intersections of each other, and a large number of strip members are arranged in a vertical and horizontal lattice shape substantially perpendicular to the radiation direction and the radiation direction, and a diagonal lattice network substantially perpendicular to the radiation direction and orthogonal to each other. In use, the mesh portion of one of the two adjacent rotating disks is a vertical and horizontal lattice-like mesh portion, and the mesh portion of the other rotating disk is an oblique lattice. By forming the net portion in the shape of a circle, the projections protruding from the net portion of one rotating disk are directed in the direction of the space between the strip members of the net portion of the other rotating disk.

[0013]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing an example of a rotating disk type sewage treatment apparatus of the present invention, FIG. 2 is a plan view of the rotating disk type sewage treatment apparatus of the present invention shown in FIG. 1, and FIG. It is a partial notch side view of the rotating disk type sewage treatment apparatus of the invention. In FIGS. 1 to 3, reference numerals 10 and 10 denote rotating disk blocks in which a plurality of rotating disks 1, 1... Are provided at intervals, and the rotating disk blocks 10 and 10 are supported by bearings 2. Mounting shaft 31 having a rectangular cross section of rotating shaft 3
, And the bearing 2 is attached to a side wall of the semi-cylindrical processing tank 4. 101 is a support plate provided on both sides of the rotating disk block 1.

A sprocket wheel 32 is mounted on the rotating shaft 3, and the sprocket wheel 32 is connected by a chain 63 to a sprocket wheel 62 mounted on a drive shaft 61 of a variable speed reducer 6 directly connected to the motor 5.
The rotation of the motor 4 is reduced by the variable speed reducer 5, and the rotation of the reduced drive shaft 51 is changed to a sprocket wheel 52,
The power is transmitted to the rotating shaft 3 by the chain 54 and the sprocket wheel 32, and each rotating disk 1, 1.
Is to be rotated.

FIG. 4 shows a fan-shaped member 11 constituting the rotating disk 1.
FIG. 5 is a sectional view taken along line VV of FIG. 4, and FIG. 6 is an end view taken along line VI-VI of FIG. The rotating disk 1 is constituted by connecting four fan-shaped members 11 shown in FIG.

As shown in FIG. 4, the fan-shaped member 11 has substantially radially extending linear portions 12, 12 on both sides thereof, and three substantially radially extending linear portions 13, 14, 15 therebetween, and an arcuate portion on the outer periphery. 16 and V-shaped portion 17 at the inner edge and two arc portions 1 between them
Twelve net portions 19a, 19 divided by 8, 18
b .. are provided. Each of the net portions 19a and 19b is provided with a lattice net by a number of orthogonal strip portions 191 and 191. As shown in FIG. 5, each of the strips 191, 191,.
A projection 192 is provided to project in a direction perpendicular to the longitudinal direction of.

Each net portion 1 between the linear portion 12 and the linear portion 13
9b, the strip portions 191, 191...
2 is directed obliquely. Similarly, in each net portion 19b between the linear portion 14 and the linear portion 15, the strip portions 191 are directed obliquely to the linear portion 14. That is, the strips 191 are formed in oblique lattice meshes in each net portion 19b between the linear portion 12 and the linear portion 13 and in each net portion 19b between the linear portion 14 and the linear portion 15. Is provided.

Further, in each mesh portion 19a between the linear portion 13 and the linear portion 14, a strip portion 191 in two orthogonal directions,
One of the strips 191 is directed parallel to the longitudinal direction of the linear portion 14, and the other strip 191 is directed in a direction orthogonal to the one strip 191. Similarly, in each mesh portion 19 a between the linear portion 12 and the linear portion 15, one of the orthogonal two-way strip portions 191, 191 is connected to the longitudinal direction of the linear portion 12. The other strip 191 is oriented in parallel, and is oriented in a direction orthogonal to the one strip 191. That is, the strips 191 are provided on the net portions 19a between the linear portions 13 and 14 and on the net portions 19a between the linear portions 12 and 15 with the linear portions 12 and 14. Is provided with a vertical and horizontal lattice-like net which is parallel or orthogonal to the longitudinal direction.

Reference numeral 181 denotes a connecting rod insertion through hole provided at the intersection of the linear portion 13 and the linear portion 15 with the arc portion 18.

The rotating disk 1 is constructed by connecting the sector members 11 shown in FIGS. 4 to 6, and the center of the rotating disk 1 is attached to the rotating shaft 3 as shown in FIGS. It is attached to the shaft 31 and the support plate 101 by a mounting bracket 32 and a bolt / nut 33.

As shown in FIG. 9, each rotating disk 1, 1,...
The connecting rod 182 is inserted through the connecting rod insertion through hole 181 of
At the end of the connecting rod 182, it is attached to the support plate 101 by bolts and nuts 183.

In two adjacent rotating disks 1, a mesh portion 1 forming a vertical and horizontal lattice-like mesh of one rotating disk 1
9a and a net portion 19b forming an oblique grid net of the other rotary disk 1 are arranged adjacent to each other, and form a vertical and horizontal grid net of one rotary disk 1 as shown in FIG. Net 1
The projection 192 of 9a is disposed so as to face the space surrounded by the strips 191 of the net portion 19b forming the oblique lattice network of the other rotating disk 1, and the oblique lattice of the other rotating disk 1 is formed. The projections 192 of the net portion 19b forming the net are arranged so as to face the space surrounded by the strips 191 of the net portion 19a forming the vertical and horizontal grid net of one rotating disk 1.

In the sewage treatment apparatus of the present invention shown in FIGS. 1 to 9, as described above, each of the rotating disks 1, 1,... Mesh portions 19a and 19b are provided, and a projection 192 is protruded at an intersection of the strip members 191 and protruded from one of the two rotating disks 1 adjacent to each other. The projection 192 is a strip member 19 of the mesh portion 19a, 19b of the other rotating disk 1.
Since it is directed in the direction of the space between 1 and 191, the following operation and effect can be obtained. That is, since the surface area per unit volume is large and the oxygen supply power to the wastewater by the aeration effect by the projection 192 is large, the wastewater treatment efficiency is high. Also, rotating disk 1
There is no deterioration of the treated water due to the simultaneous peeling of the biofilm from the biofilm, the gaps between the biofilms are formed uniformly, and there is no clogging due to excessive adhesion of the biofilm.

Therefore, the sewage sufficiently contacts the aerobic bacteria attached to the rotating disk 1 and is sufficiently treated by the aerobic bacteria.
Operation and maintenance costs are reduced.

Example 1 Sewage was treated using the sewage treatment apparatus shown in FIGS. The length L of the rotating shaft 3 is about 1 m. Capacity of sewage treatment tank 4: about 100 liters. The diameter D of the rotating disk 1 is 500 mm. Rotation speed of the rotating disk 1: 13 rpm Peripheral speed of the rotating disk 1: 20 m / min. Immersion ratio of rotating disc 1 in wastewater: about 40%. The thickness T of the strip member 191 of the rotating disk 1 is 4 mm (FIG. 5). The length L5 of the strip member 191 of the rotating disk 1 is 10 mm (FIG. 5). The length L3 of the projection 192 of the rotating disk 1 = 7 mm (FIG. 5). The distance L4 between the rotating disks 1 and 1 is 10 mm (FIG. 9). The number of rotating disks 1 in the rotating disk block 1 is 20
Sheet. The total number of rotating disks 1 is 40. The fan-shaped member 19 constituting the rotating disk 1 is made of polypropylene and is formed by injection molding.

[Comparative Example 1] As described in Japanese Utility Model Publication No. 58-6559, sewage treatment provided with a rotating disk provided with corrugations having peaks and valleys along the circumferential direction. The device was used. The rotating disk is a polyethylene sheet having a thickness of 2 mm formed by a vacuum forming method to form a rotating disk having an area expansion ratio of about 25% in projected area ratio, which is fused at 20 mm intervals for 2 blocks, for a total of 40 blocks. The sheets were set on a rotating shaft.

[Evaluation] The dissolved oxygen was measured by polarography.
Using a DO meter, add sulfuric acid as a catalyst in a water tank in advance.
Add a trace amount of copper and use anhydrous sodium sulfite as a deoxidizer
Add about 10 grams to completely consume dissolved oxygen (DO)
After that, start rotation and increase the dissolved oxygen
I asked. This is plotted on a semilogarithmic graph, and the straight line
After confirming the properties, KLa (overall oxygen) was calculated according to the following equation (1).
Transfer capacity coefficient) was calculated. KLa = 2.303 / (t)_Two-T₁) [Log (C_S-Ct₁) / (C_S−C t_Two) (1) C_SIs the saturation concentration of oxygen at that temperature (mg / l
Ct) ₁, Ct_TwoIs the measurement time t
₁, T_TwoIs the dissolved oxygen concentration at By the way, the coefficient K
La is the mass transfer coefficient in the activated sludge aeration oxygen supply.
The size, shape, and aeration of the sewage treatment tank used for the test
Apparatus shape, air volume, etc.
It is a coefficient that includes all conditions such as shape, number of sheets, and rotation speed.
The temperature was 22C. According to the wastewater treatment apparatus of the present invention according to Embodiment 1, KLa =
12.0hr^-1 According to the wastewater treatment apparatus according to Comparative Example 1, KLa = 8.5
hr^-1 That is, the sewage treatment apparatus of the present invention according to Example 1 is compared with Comparative Example 1.
Oxygen supply is about 40% better than wastewater treatment equipment
Was. The rotating circle of the sewage treatment apparatus of the present invention according to the first embodiment.
The effective surface area of the plate is about 21 m for 40 sheets^TwoAnd Comparative Example 1
The effective surface area of the rotating disk is about 20m for 40 sheets^TwoIt is.

[Example 2] Sewage is wastewater from a noodle-making factory, and its properties are as follows. Water volume: 800 m ³ / day. BOD: 700 mg / liter. COD: 520 mg / l. TN: 60 mg / liter. Due to lack phosphorus as nutrients, initially rising disodium hydrogenphosphate _{(NaHPO 4 · 12H 2 O)} 30k
g / day, and thereafter the weight was reduced to 10 kg / day. The length L of the rotating shaft 3 is about 3.8 m. Capacity of sewage treatment tank 4: about 15 m ³ . The diameter D of the rotating disk 1 is 1200 mm. Rotational speed of rotating disk 1: 10 rpm Peripheral speed of rotating disk 1: 40 m / min. Immersion ratio of rotating disc 1 in wastewater: about 40%. The width L2 of the rotating disk block 1 is 600 mm. Number of rotating disk blocks 1: 5 units. Others are the same as the first embodiment. Sewage was treated by using two such wastewater treatment devices in series × 2 series, that is, four units.

[Comparative Example 2] A sewage treatment apparatus provided with a rotating disk having the same shape as that of Comparative Example 1 was used. However, six rotating disks having a diameter of 3.6 m and a rotating shaft length of 7.5 m were used.

[Evaluation] As a result of treating the sewage by the sewage treatment apparatus of Example 2 and Comparative Example 2, the quality of the supernatant liquid after sedimentation was as follows. BOD: 25 mg / liter. COD: 43 mg / liter. Nitrogen was partially nitrified. BOD removal rate is 95%
Was over. That is, the sewage treatment apparatus of Example 2 was able to achieve the same effect with a 1/4 installation area of the sewage treatment apparatus of Comparative Example 2.

[Example 3] Sewage is marine processing wastewater (wastewater from a "Kamaboko" manufacturing plant). The average properties of concentrated sewage are as follows. Water volume: 60 m ³ / day. BOD: 2500 mg / liter. COD (Cr): 3200 mg / liter. SS: 640 mg / liter. Hexane extract: 280 mg / l. TN: 180 mg / liter. TP: 65 mg / liter. The sewage treatment apparatus of the present invention is as follows. The length L of the rotating shaft 3 is about 2.4 m. The diameter D of the rotating disk 1 is 1200 mm. Rotation speed of rotating disk 1: 10 rpm Width L2 of rotating disk block 1 = 600 mm. Number of rotating disk blocks 1: 3 units. Using three such sewage treatment devices arranged in series,
Sewage was treated.

COMPARATIVE EXAMPLE 3 Five rotating disk devices having the same rotating disk as in Comparative Example 2 and having a diameter of 2.4 m and a shaft length of 5 m were used.

[Evaluation] The following numerical values were obtained as a result of processing by the rotating disk apparatus according to Example 3 and Comparative Example 3. BOD: 80 mg / liter. COD (Cr): 120 mg / liter. TN: 110 mg / liter. In the rotating disk device according to the third embodiment, the same effect can be obtained with one-third the installation area of the rotating disk device according to the third comparative example.

Example 4 Living wastewater from an apartment house was treated. Average properties of wastewater are as follows. Water volume: 100 m ³ / day (400 people). Average properties of wastewater are as follows. BOD: 220 mg / liter. COD: 180 mg / liter. TN: 38 mg / liter. TP: 12 mg / liter. The sewage treatment apparatus of the present invention is as follows. The length L of the rotating shaft 3 is 1.8 m. The diameter D of the rotating disk 1 is 1200 mm. Rotation speed of rotating disk 1: 10 rpm Width L2 of rotating disk block 1 = 600 mm. Number of rotating disk blocks 1: 2 units.

[Comparative Example 4] A rotary disk device having the same rotary disk as that of Comparative Example 2 and having a diameter of 2.4 m and a shaft length of 4.5 m was used.
Used the table.

[Evaluation] In the rotating disk apparatus of Example 4, nitrification was promoted by only one apparatus. Thereafter, the apparatus was treated with a fully submerged denitrifying disk (diameter: 600 mm, shaft length: 1.8 m).
TN: 80% removal rate was obtained. In the rotating disk device of Comparative Example 4, it was impossible to oxidize ammonia nitrogen to nitrate nitrogen with only one unit.

Example 5 A flow rate of 6 m ³ / Hr (maximum) was branched off from a main pipe of a factory wastewater containing phenol and treated. The treatment targets are a COD removal rate of 70% and a phenol removal rate of 95%. The properties of the wastewater are as follows. BOD: 110 mg / liter. COD: 110 mg / liter. Phenol: 10 mg / liter. Hexane extract: 50 mg / l. The sewage treatment apparatus of the present invention is as follows. The length L of the rotating shaft 3 is 2.1 m. The diameter D of the rotating disk 1 is 1200 mm. The width L2 of the rotating disk block 1 is 500 mm. Number of rotating disk blocks 1: 3 units.

Comparative Example 5 A rotating disk type sewage treatment apparatus was used in which bristles synthetic fibers were processed into a net shape and integrated with a disk-shaped support and fixed to a number of rotating shafts. Length of sewage treatment tank: 2.7 m Disk diameter: 2 m Number of disks: 24 (surface area: 1900 m ² ) Rotation speed: 6 rpm

[Evaluation] The results of treating wastewater with the wastewater treatment apparatuses of Example 5 and Comparative Example 5 were as follows. COD: 20-40 mg / l. Phenol: 2 mg / liter or less. The sewage treatment apparatus of Example 5 was much smaller than the sewage treatment apparatus of Comparative Example 5 and achieved similar results. In the sewage treatment apparatus of Comparative Example 5, it was necessary to constantly blow air from a pipe provided at the bottom of the sewage treatment tank in order to remove thickened sludge. There was no need for air blasting because the film spontaneously separated.

Although the embodiment of the present invention has been described with reference to the drawings, the specific configuration of the present invention is not limited to the illustrated embodiment, and the design change within a range not departing from the gist of the present invention. Are included in the present invention.

For example, instead of forming the rotating disk 1 by connecting four fan-shaped members 19 as in the illustrated embodiment, it is formed by connecting two or eight fan-shaped members. It is also possible to use a disk-shaped member integrated from the beginning without connecting a plurality of fan-shaped members.

[0042]

According to the rotary disk type sewage treatment apparatus of the present invention, since the efficiency of sewage treatment is high, pollutants of sewage can be efficiently removed. Also, the operation and maintenance cost is low because the stability of the sewage treatment is high.

Further, in the rotating disk according to the present invention, when used, the efficiency of sewage treatment and the stability of sewage treatment are high, the sewage treatment performance is excellent, and the operation and maintenance cost is low. In addition, since the rotating disk can be formed by a single type of mold, manufacturing costs can be reduced.

In the rotating disk according to the third aspect of the present invention, in use, the mesh portion of one rotating disk of two adjacent rotating disks is formed into a mesh portion of a vertical and horizontal lattice, and the other is used. By making the mesh portion of the rotating disk a slanted grid-like mesh portion, the projections protruding from the mesh portion of one rotating disk are directed in the direction of the space between the strip members of the mesh portion of the other rotating disk. Therefore, the sewage treatment apparatus according to claim 1 can be easily assembled.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing an example of a rotary sewage treatment apparatus of the present invention.

FIG. 2 is a plan view of the rotary sewage treatment apparatus of the present invention shown in FIG.

FIG. 3 is a partially cutaway side view of the rotary sewage treatment apparatus of the present invention shown in FIG.

FIG. 4 is a front view showing an example of a fan-shaped member.

FIG. 5 is an end view taken along line VV in FIG. 4;

FIG. 6 is a sectional view taken along line VI-VI in FIG. 4;

FIG. 7 is a sectional view showing the vicinity of an end of a rotating shaft of the rotary sewage treatment apparatus of the present invention shown in FIG. 1;

FIG. 8 is a side view showing the vicinity of the end of the rotating shaft shown in FIG. 7;

FIG. 9 is an enlarged sectional view of a connecting portion of a rotating disk of the rotating sewage treatment apparatus of the present invention shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotating disk 19a, 19b Net part 191 Strip member 192 Projection 2 Bearing 3 Rotating shaft 4 Sewage treatment tank 5 Motor 6 Variable speed reducer

Claims (3)

[Claims] 1. A plurality of rotating disks are attached to a rotating shaft at intervals, and each rotating disk is provided so as to be partially immersed in sewage in a treatment tank and rotated, and the sewage is rotated by a rotating disk. A rotating disc type sewage treatment apparatus for treating sewage by contacting aerobic bacteria adhering to a board, wherein each rotating disc is provided with a number of strip members having different directions arranged side by side. A protrusion is provided at the intersection of the strip members, and the protrusion protruding from one of the two rotating disks adjacent to the other rotating disk is a thinner mesh portion of the other rotating disk. A rotating disk type sewage treatment apparatus characterized in that it is directed in the direction of the space between the one-piece members. 2. A rotary disk used in the rotary disk type sewage treatment apparatus according to claim 1, wherein each rotary disk has a plurality of strip members having different directions arranged in parallel. And a projection protruding from the intersection of the strip members. 3. A rotating disk used in the rotating disk type sewage treatment apparatus according to claim 1, wherein each rotating disk is formed with a plurality of strip members having different directions arranged side by side. Is provided, and a projection is provided at the intersection of the strip members. A large number of strip members are substantially in the radial direction and a vertical and horizontal lattice-shaped net portion orthogonal to the radial direction. A rotating disk having an oblique lattice net portion orthogonal to the rotating disk.